JS: Function Name Property

Every function has a own string property "name".

// every function have a own property string key "name"

// arrow function
console.assert(
 Object.hasOwn((x) => x + 1, "name"),
);

// function defined by keyword function
console.assert(
 Object.hasOwn(
  function ff(x) {
   return x + 1;
  },
  "name",
 ),
);

Value of function name property

Arrow function

// value of function name property

// anon arrow function name is empty string
console.assert(
 (() => []).name === "",
);

// arrow function assigned to var. name is the var name.
const ff = (x) => x;
console.assert(ff.name === "ff");

Function defined by the keyword function

// keyword function
function kwf() {
 return 3;
}
console.assert(kwf.name === "kwf");

// keyword function as function expression.
// if name appears in the function part, that is the name
const fexp = function gg() {
 return 3;
};
console.assert(fexp.name === "gg");

// the name is the variable if no name appears in the function part
const fff = function () {
 return 3;
};
console.assert(fff.name === "fff");

Name property not writable

// function name property not writable

const ff = (x) => x;

try {
 ff.name = "yes";
} catch (xerror) {
 console.log(xerror);
}
// TypeError: Cannot assign to read only property 'name' of function '(x) => x'

Class constructor with property key "name"

if you have a class that already have a name field, it is not overwritten.

class Dog {
 static name = "hoho";
}

console.log(Dog.name);
// hoho